U.S. Pat. No. 3,608,734, Schneider, the disclosure of which is hereby incorporated by reference, as well as Schneider's subsequent published European Patent Application 0 032 829, describe plate filters in which a stack of filter plates with surrounding rims have a filter web material located therebetween. Two, each, of the filter plates are separated by the filter material to form, at one side of the filter material, an inlet chamber and, on the other side of the filter material, an outlet chamber for a fluid to be filtered, upon passing through the filter material. Typically, the fluid is a liquid which is guided to the inlet chamber, beneath the lower surface of an upper plate, then passing through the filter material and into the outlet chamber formed by the upper surface of the next lower filter plate. All the inlet chambers as well as the outlet chambers are coupled to respectively common inlets and outlets, for example inlet and outlet manifolds.
The filter material is supplied in form of a web, and can be easily replaced by moving the filter material through the filter chamber. This is done by a periodically operating transport arrangement in which a portion of filter material, which has become used and requires replacement, is rolled away from the respective filter chamber and a new portion of filter material is introduced.
To permit ready movement of the filter material, it is supplied in web form, for example from rolls, similar to paper webs or the like. The plates of the stack of filter plates are first separated from each other by an apparatus which, additionally, after separation and after movement of the web of filter material, presses the plates against each other, with the filter material web interposed. The edges of rims of the respective plates forming the inlet and outlet chambers pinch or clamp the filter web material therebetween. This clamping of the filter material web provided for sealing of the inlet and outlet chambers from each other. A circumferential groove adjacent the edge of the plate is provided to collect any leakage fluid, which then can be removed by a suitable pump.
Plate filters of this type can be uesd with additional auxiliary materials, for example siliceous earth, or other types of diatomaceous earth. Use of auxiliary filter material, for example siliceous earth, causes formation of a filter cake in the inlet chamber. Usually, the filter web material is located horizontally between the respective plates. The filter cake on top of the web is removed, periodically, together with the portion of the filter web from the plate filter upon separation of the filter plates; a transport apparatus then transports the web material together with the accumulated filter cake out from the then separated filter chambers.
The referenced U.S. Pat. No. 3,608,734 describes a filter web transport arrangement including a gripping arrangement for the web material having pointed pins which penetrate within the filter web material to transport it through the filter structure, when the plates are separated. The pointed or prickly pins damage the filter web so that it can be used only once. The European Patent Application 0 032 829 describes a transport arrangement for filter web material having a transport roller and a clamping or pinch or counter roller. The counter roller has a plurality of disks associated therewith which can penetrate within the filter cake and are provided to press the filter web against the transport roller to ensure that the filter web will be reliably carried along with the transport roller.
The used filter web, together with the filter cake, can be transported to a reception container.
It may occur that, upon transporting filter material webs through the plate filter, the webs will skew with respect to the edges of the filter plates. Transporting any moving web, unsupported, over a substantial distance is difficult, and it is difficult to avoid skewing of the web.
If the filter material web is skewed with respect to the edges of the filter plates, the filter web may not be securely clamped throughout the circumference of the filter plates when they are pressed against each other, so that liquid to be filtered can escape, running out of the plates and to the floor surface on which the filter structure is placed. Thus, replacement of a section of filter web either requires continuous operator supervision to permit correction of any possible skewing of the web and to effect immediate correction; or automatic sensing and control apparatus must be provided which sense the running direction and any deviation from a predetermined path of the filter web, and reposition the filter web. Such apparatus is complex and expensive and requires continuous maintenance for proper operation.
The plate filters as described remove any filtrate or filter cake together with the filter web; the filter cake is not separated from the web after a section of filter web is replaced within the filter structure. This makes it very difficult to re-use the filter material web as well as to clean, recycle and reuse the siliceous earth; subsequent later separation of siliceous earth from filter material is difficult if not impossible.